question_answer

Why does rain water normally have a \[pH\] of about 5.6? When does it become acid rain?

Answer:

                Normally rain has a \[pH\]of about 5.6 due to dissolution of \[C{{O}_{2}}\] of the atmosphere into it \[(C{{O}_{2}}+{{H}_{2}}O\xrightarrow{}{{H}_{2}}C{{O}_{3}}\rightleftharpoons 2{{H}^{+}}+CO_{3}^{2-}).\]  When the \[pH\] of rain falls below 5.6, it becomes acid rain.